The present invention is related to and claims priority under 35 USC xc2xa7119 from German patent application number 10030606.5 filed on Jun. 21, 2000.
The invention relates to a switched-mode power supply including at least one capacitor and including a transformer having a plurality of windings.
U.S. Pat. No. 5,153,812 discloses a so-called LC element having an integrated inductance and capacitance. It alternately comprises planar electrodes and insulating layers. These alternating layers are wound so as to form a spiral coil. This LC element is used as a filter.
It is an object of the invention to reduce the number of electrical parts such as capacitors and coils in a switched-mode power supply so as to enable a simple and low-cost production in large quantities.
According to the invention this object is achieved in that the capacitor is integrated in the transformer by means of at least one multi-layer foil winding and this foil winding of the transformer consists of a plurality of planar conductive electrodes which, alternately with an insulating dielectric foil, are stacked onto each other to form an electrode stack.
In this manner the required capacitors can be integrated in the transformer of the switched-mode power supply without a high cost. This applies both to the resonance capacitor in a switched-mode power supply constructed as a resonant converter, and to the smoothing capacitor, which takes the form of a separate electrolytic capacitor in conventional switched-mode power supplies.
An embodiment has the advantage that the electrical parameters of the transformer can be varied by means of a core of a permeable material without the windings being changed. In this way it possible to realize, for example, an additional stray inductance in a simple manner.
An embodiment relates to a star arrangement of the integrated capacitors is obtained in that each of the individual electrodes only has a star point electrode as counter-electrode and does not have any further separate electrode. The star arrangement permits an adaptation to frequently used circuits in switched-mode power supplies, which often include a star arrangement of capacitances.
An embodiment leads to an increase of the integrated capacitance of a switched-mode power supply in accordance with the invention owing to the parallel-connected electrodes and capacitors. Since the layered electrodes have properly accessible contacts at their ends the electrodes can simply be electrically interconnected in an alternating fashion, as a result of which the desired parallel connection of the capacitors is obtained.
An embodiment enables a large-area contact between interconnected electrodes to be obtained, as a result of which the electrical resistance between the electrodes is reduced. Moreover, large-area contacts allow a simple automatic production with a low risk of poorly conducting electrical connections.
An embodiment has the advantage that the individual turns of the winding are electrically insulated with respect to one another in a reliable and simple manner. At the same time, this provides further possibilities of influencing the dielectric characteristics of the device, notably of the integrated capacitances.
An embodiment yields advantages in the fabrication of the electrodes. The electrodes, which are electrically insulated with respect to one another, can be manufactured by simple vapor deposition of a metal layer on one or both sides of the insulating foil. Vapor deposition enables particularly thin and, consequently, space-saving electrodes to be manufactured.